With reference to FIG. 1, a conventional boost circuit for driving a backlight module of a liquid crystal display device mainly has an input power Vin, a first winding L1 connected to the input power Vin, a second winding L2 connected to the first winding L1, a diode D2 connected between the second winding L2 and an output capacitor, and a transistor switch Q1.
The boost circuit uses the action of repeatedly switching on-and-off of the transistor switch Q1 to control the first winding L1 to output an forward-biased voltage, and then to raise the voltage with the number of windings of the second winding L2 being larger than the number of windings of the first winding L1, so that the output capacitor can provide an output voltage higher than the input voltage Vin to the backlight module on a load end.
Foregoing boost circuit implements a boosting effect that the output voltage is higher than the input voltage. However, since the boost circuit uses the diode D2 for rectification, as the circuit outputs a large current, power consumption of the diode will become higher and cause the efficiency of the boost circuit to decrease and a problem of heat dissipation. If the boost circuit uses a MOSFET for rectification, the circuit needs to be driven with a floating ground isolation, which causes design of the circuit to be more complicated.
Hence, it is necessary to provide a self-driven synchronous rectification boost converter having high step-up ratio to overcome the problems existing in the conventional technology.